1. Field of the Invention
The present invention relates to a relaying apparatus, and in particular to a relaying apparatus which detects a congested or uncongested state to perform a data flow control.
2. Description of the Related Art
FIG. 9 shows an arrangement of a conventionally known relaying apparatus used in a LAN (Local Area Network) i.e. collection of computers that share data and resources in one primary location. A relaying apparatus 1 is connected to a backbone LAN 3 through an up-link 2 and is also connected to a second relaying apparatus 7 through a stack-link 8.
The internal arrangements of the relaying apparatus 1 and the relaying apparatus 7 are common, so that taking the relaying apparatus 1 as an example for the sake of description, ports (e.g. Input/Output ports) 11 which can be connected to terminals (not shown) such as personal computers and switches/repeater hubs are connected to a switching portion 12. The ports 11 can automatically recognize the bandwidth of the interfaces (i.e. the 10BASE-T (10 Mbps) and the 100BASE-TX (100 Mbps)) according to the IEEE802.3 standard.
This IEEE802.3 standard deals with Ethernet which is the most widely used LAN technology. The above-noted 10BASE-T is the original and most common version of Ethernet and denotes a peak transmission speed of 10 Mbps. Newer versions of Ethernet called “Fast Ethernet” and “Gigabit Ethernet” support data rates of 100 Mbps and 1 Gbps (1000 Mbps), respectively, including the standards of the 100BASE-TX as above-noted and the 1000BASE-X.
An output buffer 13 is provided between the switching portion 12 and the up-link 2, and the number of frame staying at the output buffer 13 is monitored by a monitoring portion 14 so that the state of the up-link 2 may be always monitored.
In addition, an output buffer 15 is provided between the switching portion 12 and the stack-link 8, and a stack-link monitoring portion 16 is connected to the output buffer 15 in the same way as the up-link 2 so that the number of frame staying at the output buffer 15 before the stack-link 8 can be always monitored.
The monitoring portions 14 and 16 are connected to a flow controller 17, so that when the monitoring portions 14 and 16 respectively detect the congested state of the links 2 and 8 the congested state is notified to the flow controller 17.
It is to be noted that an interface 18 is provided between the output buffer 13 and the up-link 2 as well as an interface 19 is provided between the output buffer 15 and the stack-link 8.
Furthermore, although this arrangement illustrates only the case where frames are outputted from the relaying apparatus 1 to the up-link 2 and the stack-link 8, input portions and the like necessary for the case where the frames are conversely inputted from the up-link 2 and the stack-link 8 are not illustrated for the sake of simplifying the figure.
The congested state which may occur in such a conventional relaying apparatus will be described more specifically referring to FIGS. 10 and 11.
Firstly, in the example of FIG. 10, only six arrows are shown toward the up-link 2. However, assuming that the interface 18 of the up-link 2 is a “Gigabit Ethernet” type (ex. 1000BASE-X) as above-noted and the ports are the “Fast Ethernet” type (ex. 100BASE-TX (100 Mbps interface)) as above-noted, when the ports 11 having terminal ports more than ten on the calculation try to simultaneously communicate with the up-link 2 with a full wire (upper limit of a transmission line capability) the processing capability of the up-link interface 18 is physically exceeded, resulting in a congested state.
In the example of FIG. 11, six arrows are shown from a part of terminals 4 connected to the ports 11 of the relaying apparatus 1 to the interface 18, and further two arrows are shown from a part of terminals 9 connected to ports 71 in a second relaying apparatus 7 connected to the relaying apparatus 1 through the stack-line 8, so that eight arrows are shown in total. Likewise in this case, when more than ten terminal ports 11 and 71 on the calculation are simultaneously connected to the up-link 2 with the full wire, the processing capability of the interface 18 is physically exceeded, resulting in a congested state.
When such a congested state occurs and the notification thereof is provided to the flow controller 17 from the monitoring portion 14 or 16, the flow controller 17 controls to either transmit a congestion signal to the switching portion 12 or substantially stop the following communication by intentionally generating a collision state in the ports 11 in case that the above-mentioned interfaces 10BASE-T and 100BASE-TX are a half-duplex communication type.
Also, in the above-mentioned international standard IEEE802.3X, when the number of buffer staying frame exceeds a fixed threshold value, a “pause” frame is transmitted to the link connected to the ports 11, so that the control to stop the transmission of frame is performed on the reception side of the pause frame until a timer expires.
In the control method of transmitting the congestion signal or generating the compulsory collision state as is the case with the above-mentioned conventional relaying apparatus, there is a problem that the inputs to the ports must be entirely stopped.
Also, in the international standard IEEE802.3X, if a plurality of relaying apparatuses are mutually connected as shown in FIG. 9, a flow control by the whole of a relaying apparatus can be performed, while the flow control by an individual port can not. In addition, if the flow control by the whole apparatus is performed, it is disadvantageous that the control is performed even to communications which have nothing to do with the congested state of the up-link or the stack-link such as the communication within the apparatus.